Telescope Reviews: ALERT - Comet 17/P Holmes in mega outburst

Comet Holmes as seen from South Louisiana (over the period of six consecutive nights), USA (29.36°N, -90.45°W)

Primary Instrument used : 50/600mm Asahi-Pentax f/12 achromat
Other instruments used : 8x42, 10x50, 15x70mm binoculars mounted and handheld.

-->Nights 1-6 (10/24 - 10/29)

Average NELM ~4.6 to 4.8
Average Transparency : 7/10max
Average Seeing : 5/10max
Average Temperature : 70°F
Average Relative Humidity : 61%
Average Cloud Cover : 10%
Moon Interference : Waning, 26th was the Full Moon, 11/1 is Last Quarter.
Eyepieces/Magnifications :.965" KK Orthoscopic 25mm (24x), .965" Vixen Ortho 6mm (100x), 1.25" Vixen Plossl 40mm (15x), 1.25" RKE 28mm, (21x), 1.25" Vixen Lanthanums 25,20,9mm (24x,30x,66x), 1.25" TV Nagler T1 7mm (86x), Meade 2x Telenegative barlow, Pentax .965" prism diagonal, Russell Hybrid diagonal 1.25/.965.

10-24 Night 1 Summary - Very bright, very compressed pseudo-nucleus, stellar nucleus not seen. Halo/Coma is bright but not extensive. Looks like a bright compressed globular cluster or planetary nebula, or perhaps a defocused bright planetary disc. Naked eye, the comet is easily brighter than Delta Persei and rivals Algol. The waxing moon interferes greatly, but yet the comet is easily seen. Overall color impression is very yellowish, naked eye and under magnification.

10-25 Night 2 summary - the pseudo-nucleus is bright but has faded ever so slighty since Night 1, and has expanded in size. The coma is also expanded in size, but is also not quite as bright as Night 1. To me, it looks like a bad out of focus star test. The moon is still intefering with getting the best view. Naked eye brightness is still roughly equal with Algol and brighter than Delta Persei. Overall color impression is still more yellow than white, but growing paler.

10-26 Night 3 summary - the pseudo-nucleus has grown noticeably but is now less bright in comparison to the surrounding coma which has swelled considerably. The overall size of the comet including coma in the eyepiece at 24x is now roughly the same area of M42 that is visible at the same magnification under NELM ~4.6 skies. The coma continues to expand in size and is slowly thinning out or appearing more tenuous and faint. The Full Moon interferes considerably with getting a good view. The stellar-appearing nucleus is glimpsed a few times via averted vision. Naked eye magnitude is now less than Algol and about equal with Delta Persei. Overall color impression is now more white than yellow, more of a creamy ivory (warm off-white).

10-27 Night 4 summary - nucleus has stopped growing apparently, but the coma continues to swell nearly-equally like a sphere in all directions, growing in size but dimming out in apparent brightness. Comet is now several times the size of Jupiter's disc in eyepiece at 24x. I managed to view for a short time before the moon rose, but the comet was still rather low in the sky and the background sky was not quite as dark as other nights during the observing period. The stellar nucleus was glimpsed with averted vision. And a field star was glimpsed very fleetingly with averted vision through the coma. Overall color is now a pale off-white with no significant trace yellow seen. Naked eye visibility is just a bit less or equal to Delta Persei.

10-28 Night 5 summary - overall the comet is continuing to grow is size significantly (pseudo-nucleus and coma combined), but the coma is appears thinner and fainter. Without lunar interference, the stellar nucleus is glimpsed with averted vision. The size of the comet in the eyepiece is now about 1/3rd more than night 4. Overall color impression is faint whitish-grey. Naked eye brightness is slightly less than Delta Persei.

10-29 Night 6 summary - Sky conditions were the best yet. There was a "darker period" between sunset and the comet rising into good position before the moon rose to intefere. It was higher in the sky than previous nights when I made my initial observations, and the background sky considerably darker. The comet showed much better contrast and a larger overall size than the previous nights since initial outburst early last week. Also the pinpoint nucleus could be resolved in the 2" Pentax fleetingly at low powers ~24x with averted vision only, and at 100x it was seen with direct vision some of the time. The pseudo-nucleus of the comet roughly coincided with the brightest area of the surrounding coma. The coma's "apparent disc" was was the brightest appearing since the first nights of the outburst - and it was certainly much larger. The comet in the eyepiece at 24x now resembles a large well-populated globular cluster with very few or no stars resolved. It's bigger than how M22 would look at the same power under NELM ~4.8 skies, and perhaps the same apparent size of Omega Centauri seen at a fairly-dark site. It was easily 1/5th or so the size of the nearly full moon seen through the same 24x eyepiece (.965" KK Ortho 25mm, 45° AFOV, ~1.3° TFOV). Overall color impression is now mostly white to off-white, naked eye visibility is now equal again with Delta Persei.

Overall, in my opinion, the comet has progressed through the following stages over the last six consecutive nights : INITIAL OUTBURST, OUTBURST Stage-1(10/24/07) (nearly stellar with unaided eye and in lowest power), OUTBURST Stage-2(10-25) (fuzzy/nonstellar unaided eye, much larger coma with moderate-high powers, EXPANSION(10/26/07) (very large extended coma and halo with bright relatively compact pseudo-nucleus), SLOW EXPANSION/FADE(10/27/07) (continued growth in overall size, but a slow subtle decline in surface brightness and unaided eye LM), CONTINUED EXPANSION/FADE(10/28/07) (continued growth in outer dimensions of the halo, but a general decline in brightness in the pseudo-nucleus and coma), EXPANSION/BRIGHTENING(10/29/07) (a combined brightening of the pseudo-nucleus and coma with expanded overall size and surface brightness of the extended halo) - these represent nights 1,2,3..etc., with the last one representing the apparent brightening of the comet on Night 6, which may have been helped by the much darker and more transparent nature of the moonless sky.

If the good observing weather keeps up (*knock on wood*), I plan on making new entries for nights 7+ onward. Within a few days, I should have my mount fixed and my 80/1200mm Vixen refractor back online and available.

Attached is a photo of the small scope and rig I am currently limited to. The objective glass is small, but very well-figured and the scope shows virtually no CA. Optically, it "punches above it's weight" so to speak. (the photo flash is really making the eyepiece cry!)

Regards and clear dark skies,

MikeG

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Michael Gilmer - Member of the Meteoritical Society & Collector of Falling Stars.

Galactic Stone & Ironworks - Buy/Sell/Trade Meteorites, Moon Rocks, Mars Rocks, & 35 different falls and types!

Edited by Glassthrower (10/30/07 06:00 PM)